This invention relates to a method for manufacturing leakage current-proof epoxy resin molded materials from epoxy resin mixture based on di- or polycarboxylic acid glycidyl esters, di- or polyfunctional cycloaliphatic olefinic epoxides, dicarboxylic acid anhydrides and reaction accelerators as well as, optionally, fillers and other additives.
Energy-related apparatus and installations, frequently require electrical insulating components of large volume, and having large differences in wall thickness within the individual part. The insulating material employed for that purpose is generally based on reaction resin molded materials and in particular, upon epoxy resin molded materials which usually also contain fillers. If stringent requirements exist with respect to mechanical strength, a model for such properties is represented by a standard molded material based on Araldit.RTM.B (molded material 1,000-6).
Future technical developments in the field of energy-related apparatus and installation are aimed, among other things, toward obtaining higher power per unit volume. This, however, increases the requirements with respect to the mechanical-thermal "stressability" of the insulating components. An additional requirement, for instance, for switching installations, is a high leakage current resistance corresponding to Step KA 3c or KB 600 (DIN 53 480). Moreover, open-air resistance is also required. In addition, modern production methods require economical manufacturing methods, for instance, injection molding methods.
In recent times it has been found that the selection of epoxy resins for use in the manufacture of molded materials of the above-mentioned type, must take into account the toxicological aspects of the epoxy resin selected in order to minimize potential toxicological dangers during processing. This requirement has lead to a reduction in the epoxy resin compounds available for technical use and thereby, to a drastic limitation on the synthesis of reaction resin polymer lattices, and particularly on such reaction resin polymer lattices which could be used to provide molded materials having the properties discussed-above.
The foregoing also applies to injection-moldable filler-containing epoxy resin systems available for a number of years, which are based on 1,3-bisglycidyl-5,5-dimethyl hydantoin/1-glycidyl-3-beta-glycidyl oxypropyl-5,5-dimethylhydantoin/1-glycidyl-3-beta-hydroxypropyl-5,5-dimeth ylhydantoin with the isomer mixture of methyltetrahydrophthalic-acid anhydride. With this system, for instance, insulating materials and parts, suitable for use in medium-voltage switching installations, can be manufactured which meet the requirements raised above. It has been found, however, that the chemical basis of these systems must be replaced for toxicological reasons.
Therefore, the problem which arose was to find an injection-moldable resin system based on epoxy resins which would be available for the long term, and which are toxicologically unobjectionable, which is at least equivalent in electrical and mechanical-thermal respects when compared to the hydantoin system mentioned above.
It is known from the technology of epoxy resins that resins of different structure (E1, E2 . . . ) and polyaddition components such as dicarboxylic acid anhydrides of different structure (S1, S2 . . . ) can be combined in order to form reaction resin lattices, while observing stoichiometric boundary conditions, as to type and weight content, which are variable within wide limits. The properties of the molded materials expected from combination systems (E1, E2 . . . and S1, S2 . . . ) can often be estimated from the molded material properties of the boundary systems (such as E1/S1, E2/S2, E1/S2, E2/S1) and the weight contents employed, while observing stoichiometric boundary conditions and adequate reaction conditions. However, the knowledge regarding the structure and properties of epoxy resin lattices is not sufficient for quantitative estimates, so that empirical optimizing work must be conducted.
The problem confronted consisted in finding a replacement of the above-mentioned hydantoin system which has the following properties:
______________________________________ bending strength (BF) 128 N/mm.sup.2 (DIN 53 452) impact strength (SZ) 12 kJ/m.sup.2 (DIN 53 453) dimensional heat resistance 126.degree. C. (DIN 53 458) after Martens (T.sub.M) leakage current greater than 600 (DIN 53 480) resistance (KB method ______________________________________